1. Field of the Invention
The present invention relates to a method and a system for limiting or prohibiting reproducing an information signal recorded on a recording medium for example, for transmitting the analog information signal together with information for preventing reproduction, for receiving the transmitted information signal and recording it on another recording medium and an information output device used for the system.
2. Description of the Related Art
A video tape recorder (VTR) has been popularized and a large number of software reproducible by VTR is provided. Also, recently, a digital VTR, a reproducer for a digital video disc (DVD) and others have been realized, and an image excellent in image quality and tone quality and voice can be easily reproduced and can be seen and heard.
However, there is a problem that software provided as described above may be reproduced unlimitedly and various measures for preventing reproduction have been heretofore taken.
For example, there is a method of substantially preventing reproduction, utilizing difference in an automatic gain control (AGC) method between VTR for example as a recorder and a monitor picture tube for providing an image or difference in the characteristics of automatic phase control (APC) between them though the above method is not a method of directly prohibiting the reproduction of an analog video signal.
That is, for example, VTR adopts the ACC method in which a pseudo synchronizing signal inserted into a video signal is used and a monitor picture tube adopts the AGC method in which a pseudo synchronizing signal is not used. In the method of preventing reproduction by utilizing the difference in the AGC method, when an analog video signal is recorded on an original recording medium, a pseudo synchronizing signal the level of which is extremely high as a synchronizing signal for AGC is inserted and the above pseudo synchronizing signal the level of which is extremely high is inserted into a video signal supplied from VTR for reproduction to VTR for recording as a synchronizing signal for AGC.
Also, VTR adopts an APC method of using the phase of a color burst in a video signal and a monitor picture tube adopts an APC method which is different from the above APC method. In a method for preventing reproduction by utilizing difference in the characteristics of APC, when an analog video signal is recorded on an original recording medium, the phase of a color burst in the video signal is partly inverted and a video signal the phase of a color burst of which is partly inverted is output as a video signal supplied from VTR for reproduction to VTR for recording.
In the above case, in a monitor picture tube to which an analog video signal from VTR for reproduction is supplied, an image is normally reproduced without being influenced by a pseudo synchronizing signal and the inversion of the partial phase of a color burst is used for APC.
However, in VTR to which an analog video signal into which a pseudo synchronizing signal from VTR for reproduction is inserted as described above is supplied or an analog video signal the phase of a color burst of which is inverted is supplied and recorded on a recording medium, gain control based upon an input signal or phase control cannot be normally executed and a video signal cannot be normally recorded. Therefore, even if a recorded video signal is reproduced, a normal visible and audible image cannot be reproduced.
In case an analog video signal is dealt as described above, a normal visible and audible reproduced image is prevented from being obtained in place of prohibiting reproduction and the method is so-called passive reproduction prevention control.
In the meantime, in case digitized information, for example a video signal is dealt, direct reproduction prevention control such as prohibiting reproduction is executed by adding a reproduction prevention code or a reproduction prevention control signal consisting of a reproduced generation limitation code and others as digital data to a video signal and recording it on a recording medium.
FIG. 1 is a basic block diagram showing a reproducing and recording system in case the above digitized information is dealt. A digital information signal reproduced by a digital information reproducer 110 is sent to a digital information recorder 120 via a digital information transmission line 101, if the digital information signal may be reproduced, reproduction is executed and if reproduction is not allowed, reproduction is prohibited.
Reproduction prevention control information as added information is recorded in addition to digital main information on a recording medium 111 installed in the digital information reproducer 110. This reproduction prevention control information includes the prohibition and allowance of reproduction, the limitation of a generation and others as its control contents. A digital information reproducing section 112 reads an information signal from the recording medium 111, obtains reproduction prevention control information together with digital main information and sends them to the digital information recorder 120 via the digital information transmission line 101.
The reproduction prevention control signal detecting section 122 of the digital information recorder 120 detects a reproduction prevention control signal from an information signal received via the digital information transmission line 101 and judges its control contents. The reproduction prevention control signal detecting section 122 sends the result of the judgment to the digital information recording section 121.
The digital information recording section 121 converts an input digital signal to digital information suitable for recording when the result of judging the reproduction prevention control signal from the reproduction prevention control signal detecting section 122 shows that the recording of digital information input via the digital information transmission line 101 is allowed and writes the converted digital information to a recording medium 123. In the meantime, when the result of the judgment of a reproduction prevention control signal sent from the reproduction prevention control signal detecting section 122 shows that reproduction is prohibited, the digital information recording section 121 does not write input digital information to the recording medium.
Further, when the result of the judgment of a reproduction prevention control signal sent from the reproduction prevention control signal detecting section 122 shows that only the reproduction of a first generation is allowed, the digital information recording section 121 converts the above input digital signal to digital information suitable for recording, writes it to the recording medium 123, changes the reproduction prevention control signal from added information to the one which shows the prohibition of reproducing the next generation and records the changed reproduction prevention control signal on the recording medium 123. Therefore, a video signal cannot be reproduced using the reproduced recording medium 123.
If a main information signal and a reproduction prevention control signal as added information are supplied to a recorder as a digital signal as described above, in other words, in the case of digital connection, reproduction prevention control such as the prohibition of reproduction can be securely executed using a reproduction prevention control signal in the recorder.
If the digital information reproducer shown in FIG. 1 is a digital VTR for example, only a video signal and an aural signal respectively as a main information signal are converted to an analog signal via a D/A converter circuit 113 so as to monitor the reproduced video signal and aural signal and are normally supplied to a monitor picture tube via an analog output terminal 114.
Even if the reproducer is the one for digital information as described above, a reproduction prevention control signal is not included in an analog signal supplied from the analog output terminal 114. Therefore, in the case of analog connection in which an analog VTR and others are connected to the analog output terminal 114, an information signal can be reproduced.
Accordingly, it is conceivable that a reproduction prevention control signal is superimposed on a video signal and an aural signal respectively converted from digital to analog, however, it is difficult to add a reproduction prevention control signal without deteriorating the video signal and the aural signal respectively converted from digital to analog, to extract the reproduction prevention control signal from a recorder and use it for reproduction prevention control.
Therefore, in the case of analog connection, there was only a method of passively preventing reproduction using a reproduction preventing method utilizing difference in an AGC method between the above VTR and a monitor picture tube or difference in the characteristics of APC.
However, in the case of the reproduction prevention control method utilizing difference in the AGC method between the above VTR and a monitor picture tube or difference in the characteristics of APC, a video signal is normally recorded depending upon an AGC method or the characteristics of APC on the side of a recorder and a case that even passive reproduction prevention cannot be executed occurs. There may occur a problem that an image reproduced on a monitor picture tube is out of order.